Free Traffic by Tom Vanderbilt Page B

merge, they create a temporary second queue. Drivers who grow frustrated in the queued line might similarly force their way into the faster open lane. This is all a recipe for rear-end collisions, which, as it happens, are among the leading types of crashes in work zones.
    To improve things, North American engineers have responded in two basic ways. First, there is the school of Early Merge. To tackle the “forced merge” problem, Early Merge spreads out the whole merging zone. Drivers are warned by a sign several miles in advance of the “taper” that a lane drop is coming, rather than the twelve hundred feet or so in the conventional merge. “No Passing Zones” signs are often placed in the lane that will close. The earlier notice, in theory, means drivers will merge sooner and with less “friction,” as engineers politely say, and will be less surprised by a sudden queue of stopped cars. Indeed, a 1997 study of an Indiana construction site using this system showed very few forced merges, few “traffic conflicts,” and few rear-end collisions.
    Early Merge suffers from a critical flaw, however. It has not been shown to move vehicles through the work zone more quickly than the conventional merge. One simulation showed that it actually took vehicles
longer
to travel through the work zone, perhaps because faster-moving cars were being put behind slower-moving cars in a single lane sooner than they might naturally have gotten there, thus creating an artificial rolling traffic jam. An Early Merge system would also seem to require some kind of active law enforcement presence to make sure drivers do not violate the concept. As we all know, the presence of a police car on the highway has its own unique effects on traffic.
    The second school, Late Merge, was rolled out by traffic engineers in Pennsylvania in the 1990s in response to reports of aggressive driving at merge locations. In this system, engineers posted a succession of signs, beginning a mile and a half from the closure. First came USE BOTH LANES TO MERGE POINT, then a ROAD WORK AHEAD or two, and finally, at the lane drop: MERGE HERE TAKE YOUR TURN .
    The beauty of the Late Merge system is that it removes the insecurity or anxiety drivers may feel in choosing lanes, as well as their annoyance with a passing “cheating” driver. The Late Merge compresses what may normally be thousands of feet of potential merging maneuvers to a single point. There is, presumably, no lane jumping or jockeying, as the flow or speed should be no better or worse in one lane than another—hence there are fewer chances for rear-end collisions. Because cars are using both lanes to the end point, the queue is cut in half.
    The most surprising thing about the Late Merge concept is that it showed
a 15 percent improvement in traffic flow
over the conventional merge. It turns out that the Live Free crowd was right. Merging late, that purported symbol of individual greed, actually makes things better for everyone. As one of my Live Free responders had succinctly put it: “Isn’t it obvious that the best thing to do is for both lanes to be full right up to the last moment, and then merge in turn? That way, the full capacity of the road is being used, and it’s fair on everyone, rather than a bunch of people merging early and trying to create an artificial one-lane road earlier than necessary.” (Note: This does
not
apply to people “late-merging” their way to the head of queues at off-ramps and the like, as those late mergers may temporarily block an otherwise free-flowing lane of traffic, not to mention greatly irritating those already queued.)
    It’s not just North Americans who have problems with merging. The United Kingdom’s Transport Research Laboratory, in an internal report looking at new work-zone merging treatments, noted the “poor utilization of the closed lane well in advance of the taper,” which it partially attributed to “vehicles blocking this lane deliberately